JavaScript comparing two arrays

Question

Is there i way in JavaScript to compare two arrays;

This is my example.

array1 = ['jpg','png'];

array 2 = ['jpg','pdf','png','bmp'];

I my case i need if are all elements of array1 part of array2 return TRUE, or something. In case only one element of array 1 match, element in array 2 return FALSE. Order its not important. Basciclly this is validation of uploaded files, i try to removing button, if two file are not with right extension.

I try function inarray, but i think it only works with string not array

array1 compared to array2 return true and array2 compared to array1 return false? — Bharadwaj
– Bharadwaj, Commented Dec 29, 2014 at 13:18
I heard somewhere that you can just compare the toString of each array. — Mr. Polywhirl
– Mr. Polywhirl, Commented Dec 29, 2014 at 13:20
I don't think this is a duplicate of Comparing two arrays in Javascript. This question asks how to test if array1 is a subset of array2 where order doesn't matter, which seems quite different from testing the equality of two arrays. I'm not 100% sure if this is a good question (maybe it's too specific to be helpful to any likely future readers? maybe not?), but it's not a duplicate. — apsillers
– apsillers, Commented Dec 29, 2014 at 13:24
This is not duplicated at all. But it's already closed, so whatever. @Vladimir Štus here is an answer with proper validation jsfiddle.net/wxfnr2f2. Also check loxxy's answer for another working solution for your problem. — dfsq
– dfsq, Commented Dec 29, 2014 at 13:26

loxxy · Accepted Answer · 2014-12-29 13:19:37Z

2

If legacy is not a problem, Something like this would do:

var array1 = ['jpg','png','d'];
var array2 = ['jpg','pdf','png','bmp'];

var result = !array1.filter(function(a) { return array2.indexOf(a)==-1; }).length;   

// result is False

answered Dec 29, 2014 at 13:19

loxxy

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9 Comments

Paul S. Over a year ago

OP wants to check all elements are there, intersection.length === array1.length

apsillers Over a year ago

@PaulS. The code in this answer appears to be behave correctly. It eliminates items that are a match and tests for any remaining non-match items in array1 (thus a non-zero length is a failure condition, implying that something wasn't eliminated as a match).

dfsq Over a year ago

This is correct although not optimal answer. No need to check further is something is already returned -1.

apsillers Over a year ago

Per @dfsq's suggestion, a better solution might be array1.every(function(a) { return array2.indexOf(a)!=-1; }), which will return false early on the first failure (and the use of every here seems more idiomatic to me than filter, but that's a bit nitpicky).

dfsq Over a year ago

@apsillers No, my suggestion was !array1.some(function(el) { return array2.indexOf(el) == -1; });, so it never checks further is something is already -1.

|

Paul S. · Accepted Answer · 2014-12-29 13:30:20Z

0

if are all elements of array1 part of array2 return TRUE
only one element of array1 match, element in array2 return FALSE

You can think about this in two ways,

take the intersection and check the intersection is the same as the input
loop over the input and return false on the first mismatch

Here is an example of using a loop

var a = [1, 3],
    b = [1, 5],
    c = [0, 1, 2, 3, 4];

function test(needles, haystack) {
    var i;
    for (i = 0; i < needles.length; ++i) {
        if (haystack.indexOf(needles[i]) === -1) {
            return false;
        }
    }
    return true;
}

test(a, c); // true
test(b, c); // false

answered Dec 29, 2014 at 13:30

Paul S.

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Comments

KooiInc · Accepted Answer · 2014-12-29 13:40:12Z

If the result of filtering the second array with the values of the first is an array with length equal to the length of the first array, the first array is a subset of the second. You can write a function for that, or assing an extra method to Array.prototype:

var array1 = ['jpg', 'png'];
var array2 = ['jpg', 'pdf', 'png', 'bmp'];
var array3 = ['jpg', 'bmp', 'pdf'];

Helpers.log2Screen('array1 subset of array2? ', 
                    isSubset(array1, array2) ? 'yes' : 'no' );

// assign and use Array.prototype.subsetOf
Array.prototype.subsetOf = isSubsetProto;
Helpers.log2Screen('array1 subset of array3? ', 
                    array1.subsetOf(array3) ? 'yes' : 'no' );

function isSubset(arr1, arr2) {
  return arr2.filter(
          function (v) {return arr1.indexOf(v) > -1; }
         ).length == arr1.length;
}

function isSubsetProto(arr) {
    return arr.filter(
          function (v) {return this.indexOf(v) > -1; }, this
         ).length == this.length;
}

<script src="http://kooiinc.github.io/JSHelpers/Helpers-min.js"></script>

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